1. Field of the Invention
The present invention relates generally to cutting and grinding tools. In particular the present invention includes a superabrasive surface for use with circular cutting and grinding tools and a method for making the same.
2. Description of the Related Art
Materials such as granite, marble, filled concrete, asphalt and the like are typically cut using superabrasive saw blades. These blades include a circular steel disc having a work surface made up of a plurality of spaced segments about the perimeter of the disk, the segments having superabrasive surfaces for the cutting of the material. Further, plastic and glass lenses for optical devices such as eyeglasses are commonly shaped using grinding wheels which have a superabrasive work surface. The abrasive portions of these saw blades or grinding wheels usually include particles of super hard or abrasive material, such as diamond, cubic boron nitride, or boron suboxide surrounded by a filler material and/or embedded in a metal matrix. It is these abrasive particles that act to cut or grind a work piece as it is placed against a rotating work surface of the cutting or grinding tool.
The arrangement of the particles of abrasive material in the work surface is important to performance of the cutting or grinding tool. First, an unvarying or homogeneous concentration or hardness of abrasive material in a direction along the circumference of the cutting surface results in reduced cutting performance. As such it is advantageous to be able to vary the concentration or hardness of abrasive particles in the cutting surface to produce a surface of varying abrasiveness. For example, Fisher, in U.S. Pat. No. 5,518,443 for a Superabrasive Tool issued May 21, 1996, discloses a tool having a cutting surface divided in the circumferential direction into segments having varying concentrations of abrasive particles. Regions of lower concentration of abrasive material will wear faster than regions of higher concentrations of abrasive particles exposing fresh high concentration regions. These fresh regions cut more effectively than worn regions of higher concentration of cutting material thereby increasing the cutting performance of the tool.
Second, it is known in the art to form cutting surfaces in which the concentration of abrasive particles in the cutting surface varies in a direction of the axis of rotation of the abrasive tool. For example, Wiand, in U.S. Pat. No. 4,131,436 for Ophthalmic Flat Roughing Wheel, issued Dec. 26, 1978, discloses a grinding wheel in which the concentration of abrasive particles in the surface of the grinding wheel comprises layers which define a zone of high abrasive particle concentration in the axial center of the wheel with zones of lower abrasive particle concentration on either side. However, as noted above, a region of lower concentration of abrasive particles will wear down faster than a region of relatively higher concentration of abrasive particles. Thus, after a period of use, a cutting or grinding tool of the type disclosed in Wiand develops a characteristic edge pattern across the width of the cutting surface in the direction of the axis of rotation of the tool. This characteristic edge is known as the tool's wear profile.
The wear profile of a superabrasive cutting or grinding tool affects the quality of the cut performed on a work object. For example, it is likely that the type of tool disclosed in Wiand would develop a rounded, convex wear profile that has radially low spots at the outer edges of the tool in the direction of the axis of rotation of the tool and radially high spots in the center of the tool between the low spots. This type of wear profile is generally undesirable because it can produce a somewhat ragged-edge cut and the circular steel disk can be unexpectedly exposed at the radially low edges of the tool during a cut, causing unintended cutting results.
It is more desirable to have a concave wear profile wherein high spots are created at the edges of the profile and a low spot is created in the center of the profile. This type of wear profile can produce a clean-edged cut and tends not to expose the circular steel disk prematurely and allows more efficient use of abrasive material. Also, it may also be desirable to have slightly different, and more complex, cutting profiles dependent upon the work object and the type of cut desired.
Third, the life of the tool and the speed of the cut are also dependent upon the arrangement of the particles in the work surface and the composition of the work surface. A work surface in which abrasive particle are embedded in a relatively soft bond material can cut faster because the worn particles are pulled from the soft bond material relatively rapidly, exposing fresh abrasive particles. This type of work surface, however can wear relatively quickly. On the other hand, abrasive particles embedded in a relatively hard bond material can cut relatively more slowly because worn particles are not pulled from the hard bond material so quickly to expose fresh abrasive particles. This type of work surface, however, can have relatively long life.
Finally, abrasive material used in such cutting or grinding tools is relatively expensive; thus, it is desirable to reduce the quantity of abrasive material necessary without reducing the performance of the cutting or grinding tool.
As such, it is advantageous to be able to control the wear profile of a superabrasive cutting or grinding tool. Further, it is advantageous to have a work surface which will provide relatively rapid cutting with a relatively long life. Also, such a tool should be efficient and relatively inexpensive to manufacture.